Multi-photon exposure system

ABSTRACT

An exposure system includes a light source emitting a beam along an optical axis that is capable of inducing a multi-photon reaction in a resin. The exposure system further includes a resin undergoing multiphoton reaction, as well as an automated system including a monitor that measures at least one property of the beam selected from power, pulse length, shape, divergence, or position in a plane normal to the optical axis. The monitor generates at least one signal indicative of the property of the beam, and a sub-system adjusts the beam in response to the signal from the monitor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2009/034287, filed on Feb. 17, 2009, which claims priority to U.S.Provisional Application No.61/031,538, filed on Feb. 26, 2008, thedisclosures of which are incorporated by reference in their entiretyherein.

TECHNICAL FIELD

The invention relates to optical systems, and more particularly, tooptical systems suitable for use in a multi-photon exposure processutilizing a photocurable material.

BACKGROUND

Multiphoton curing processes are described in U.S. Pat. No. 6,855,478.In these processes, a layer of a multiphoton curable photoreactivecomposition is applied on a substrate and selectively cured using afocused source of radiant energy, such as an ultrafast laser beam. Amultiphoton curing technique may be used to fabricate two-dimensional(2D) and/or three-dimensional (3D) structures with micro- or nano-scaleresolution.

Using a multiphoton curing technique, a 3D structure may be constructedvoxel-by-voxel (3D volume element by 3D volume element) by controlling alocation of the focus of the laser beam in three dimensions (i.e.,x-axis, y-axis, and z-axis directions) within the photoreactivecomposition. In many cases, 3D structures are formed by curingapproximately single voxel layers (e.g., in the x-y plane), followed bymoving the focal point about one voxel length (e.g., in the z-axis), andcuring a subsequent layer (e.g., in the x-y plane). This process may berepeated until the desired structure is at least partially cured.

SUMMARY

In one aspect, the present disclosure is directed to an exposure systemincluding a light source emitting a beam along an optical axis. The beamis capable of inducing a multi-photon reaction in a resin. The exposuresystem further includes a resin undergoing multiphoton reaction, and anautomated system. The automated system includes a monitor that measuresat least one property of the beam selected from power, pulse length,shape, divergence, or position in a plane normal to the optical axis,and generates at least one signal indicative of the property of thebeam. A sub-system adjusts the beam in response to the signal from themonitor.

In another aspect, the present disclosure is directed to an exposuresystem including a light source emitting a beam along an optical axis,wherein the beam is capable of inducing a multi-photon reaction in aresin. The exposure system further includes a resin undergoingmultiphoton reaction, as well as an automated system that monitors avoxel shape within the resin. The automated system generates a signalindicative of the voxel shape, and adjusts the beam in response to thesignal.

In yet another aspect, the present disclosure is directed to an exposuresystem including a light source emitting a beam along an optical axis,wherein the beam is capable of inducing a multi-photon reaction in aresin. The exposure system further includes a resin undergoingmultiphoton reaction, and an automated system. The automated systemincludes means for monitoring a voxel shape within the resin, and meansfor adjusting the beam in response to a signal from the means formonitoring.

In yet another aspect, the present disclosure is directed to an exposuresystem including a light source emitting a beam substantially at a firstwavelength along an optical axis, wherein the beam inducespolymerization in a resin that is substantially optically transparent atthe first wavelength. The exposure system further includes a first beammonitor system, wherein the first beam monitor systems monitors a firstcharacteristic of the beam and generates a first signal. The firstcharacteristic includes at least one of a power, a shape, and a positionof the beam in a plane normal to the optical axis of the beam. Theexposure system further includes a first divergence monitor systemmonitoring a divergence of the beam; a first divergence modulationsystem adjusting at least one of a divergence and a shape of the beam;and a first power control system adjusting a power of the beam at afirst speed. The exposure system further includes a second monitorsystem, wherein the second monitor system monitors the firstcharacteristic of the beam and generates a second signal, wherein thefirst and second signals are used to adjust the first characteristic.The exposure system further includes a first shutter transmitting orblocking the beam for controlling exposure of the resin; a third monitorsystem monitoring a position of a focal point of the beam along theoptical axis; a second divergence modulation system adjusting at leastone of a divergence and a shape of the beam; a first galvanometer systemscanning the beam at a second speed not greater than the first speed,the scanning being along a first direction substantially normal to theoptical axis; a second galvanometer system scanning the beam at a thirdspeed not greater than the first speed, the scanning being along asecond direction substantially normal to the optical axis and differentfrom the first direction; an objective lens system for focusing the beamat a position within the resin; and a sample holding system for holdingand positioning the resin and reducing the effects of at least one oftemperature and vibration on the resin.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an exposure system that may beused to fabricate an article, which preferably includes a plurality ofmicrostructures or nanostructures.

FIG. 2 is a schematic block diagram of an optical system.

FIG. 3 is a schematic block diagram of beam monitor.

FIG. 4 is a diagram of a divergence modulation system.

FIG. 5 is a block diagram of an exposure control module.

FIG. 6 is a schematic block diagram of a beam incident on a half-waveplate and a polarizer.

FIG. 7 is a graph of beam power versus angle of a half-wave plate.

FIG. 8 is a block diagram of an optical scanning module.

FIG. 9 is a schematic ray diagram of an optical relay.

FIG. 10A is a schematic diagram of a system including two galvanometersand two optical relays.

FIG. 10B is a schematic diagram of a system including an objective lens,an optical relay, and a galvanometer.

FIG. 11 is a diagram of a divergence modulator.

FIG. 12 is a block diagram of an optical system.

FIG. 13 is a schematic block diagram of a power dump module.

FIG. 14 is a schematic block diagram of a beam quality camera and powermonitor.

FIG. 15 is a schematic block diagram of a dispersion module.

FIG. 16 is a block diagram of a calibration module.

DETAILED DESCRIPTION

In general, the disclosure is directed to an automated system capable ofinitiating a reaction in a multiphoton curable photoreactivecomposition. The automated system includes a number of opticalcomponents, including a monitor that measures a property of the beam anda sub-system that modifies a monitored property in response to a signalfrom the monitor. The optical components may be used alone or incombination to improve the accuracy and/or precision of the curingprocess. This enhanced accuracy makes possible the production of moreprecisely formed three-dimensional (3D) structures, particularlystructures including complex shapes or micro- or nano-scale features.The automated system also makes possible production of the accuratestructures with high throughput, which can be important for commercialuse of multiphoton curing processes.

FIG. 1 is a block diagram illustrating an exemplary automated exposuresystem that can be used to selectively initiate a reaction and/or atleast partially cure a photoreactive composition and precisely definethe features of an article. The exposure system 10 includes an opticalsystem 11, and a block diagram illustrating further details of opticalsystem 11 is shown in FIG. 2. Exposure system 10 also includes controlmodule 12, a resin 22 including a multiphoton curable photoreactivecomposition, a substrate 20 on which resin 22 is placed, a chuck 18 tosupport the substrate 20, and a stage 16 that supports the chuck 18.Together, chuck 18 and stage 16 constitute a sample holding system 15that holds and/or positions the sample (i.e., resin 22). In someembodiments, the holding system 15 can reduce the effects of at leastone environmental factor (for example, temperature and/or vibration) onthe curing process.

Optical system 11 is an optical imaging system including a light source32 (see also FIG. 2) that provides a beam of radiation pulses 26(hereinafter “beam 26”). The beam 26 is focused through a high numericalaperture objective lens (see also objective lens 114 of FIG. 8) onto animage plane 14. In FIG. 1, resin 22, substrate 20, and chuck 18 arepositioned relative to the image plane 14 in the exposure system 10 toallow formation of a latent image or at least partial curing of theresin 22.

As described in further detail below, the automated optical system 11may include modular functional elements that are selectively appliedalone or in combination to maintain and/or enhance monitoring andcontrol over the quality and positioning of a focal point 28 of one ormore beams 26. In this application the term automated refers to a systemthat, following initial set up, applies the modular functional elementswithout human intervention to monitor and/or control the position of thefocal point 28 of the one or more beams 26. The automated nature of thesystem makes it possible for the system to rapidly adjust thecharacteristics of the beam 26 (e.g., size, shape, power, pulse length,divergence and the like), as well as control the position of the focalpoint 28, to accurately and rapidly create the features of an articlewithin resin 22. In some embodiments, the automated nature of the systemmakes it possible to adjust beam characteristics and/or position in lessthan about 1 second, in other embodiments these adjustments can be madein less than about 0.1 seconds, and in other embodiments theseadjustments can be made in a time frame on the order of milliseconds.This rapid adjustment enhances the accuracy, the speed and theefficiency of article generation.

To create features within resin 22 with three dimensional resolution,the resin 22 may be substantially optically transparent to at least someof the wavelengths of the beam 26, preferably including the wavelengthsof suitable energy to initiate single or multiphoton polymerizationwithin resin 22.

For example, in a multiphoton polymerization process, when a pulse ofsufficient intensity is present within resin 22, a nonlinear processoccurs where two or more photons of radiation interact substantiallysimultaneously with resin 22. During the nonlinear interaction process,at least a portion of a photosensitizer component of the resin reachesan excited state, which induces a chemical reaction that can lead toformation of a latent image or at least partial cure of resin 22proximate focal point 28, resulting in an at least partially cured voxelof material. Focal point 28 and resin 22 may be moved in at least one ofthe x-axis, y-axis or z-axis directions relative to each other, whereorthogonal x-y-z axes are shown in FIG. 1 (the y-axis extends in adirection substantially perpendicular to the plane of the image shown inFIG. 1) to form multiple voxels within resin 22. The multiple voxelsdefine the body of the article and/or specific micro or nano scalefeatures on the article.

As described in further detail below, beam 26 may be moved along the x,y, and/or z axis directions relative to resin 22. Or, chuck 18, and thussubstrate 20 and resin 22, may be moved along the x, y, and/or z axisdirections relative to beam 26. In the alternative, both beam 26 andchuck 18 may be moved relative to each other to fabricate voxels atdifferent positions within resin 22. In embodiments in which beam 26 ismoved relative to resin 22, optical system 11 may help selectivelyposition beam 26 within resin 22 to control the position of focal point28 within resin 22 and selectively cure regions of resin 22 to definethe features of an article. In some embodiments, focal point 28 may bescanned in one dimension (e.g., a x axis, a y axis, or a z axis). Inother embodiments, the focal point 28 of beam 26 may be scanned in twodimensions (e.g., along the x-y axes, y-z axes or x-z axes). In yetother embodiments, the focal point 28 of the beam 26 may be scanned inthree dimensions (e.g., along the x-y-z axes).

The resin 22 may vary widely depending on the intended application, andincludes any suitable multiphoton curable photoreactive composition. Forexample, multiphoton curable photoreactive compositions may include areactive species, a multiphoton photo sensitizer, an electron acceptor,and other optional components. Typical multiphoton exposablephotoreactive compositions include at least one reactive species. Thereactive species may be chosen based on a wide variety of properties,including high photosensitivity, minimal change in refractive index uponexposure to beam 26, strength and toughness of the at least partiallycured resin 22, and the like.

Reactive species suitable for use in the photoreactive compositionsinclude both curable and non-curable species. Curable species aregenerally preferred and include, for example, addition-polymerizablemonomers and oligomers and addition-crosslinkable polymers (such asfree-radically polymerizable or crosslinkable ethylenically-unsaturatedspecies including, for example, acrylates, methacrylates, and certainvinyl compounds such as styrenes), as well as cationically-polymerizablemonomers and oligomers and cationically-crosslinkable polymers (whichspecies are most commonly acid-initiated and which include, for example,epoxies, vinyl ethers, cyanate esters, etc.), and the like, and mixturesthereof.

The photoinitiator system may be a multiphoton photoinitiator system, asthe use of such a system enables polymerization to be confined orlimited to the focal region of a focused radiation beam 26. Such asystem preferably is a two- or three-component system that includes atleast one multiphoton photosensitizer, at least one photoinitiator (orelectron acceptor), and, optionally, at least one electron donor. Suchmulti-component systems can provide enhanced sensitivity, therebyreducing the exposure required to effect photoreaction of thephotoreactive composition. This allows exposure in a shorter period oftime and reduces the likelihood of problems due to relative movement ofthe resin 22 and/or one or more components of the optical system 11.

Preferably, the multiphoton photoinitiator system includesphotochemically effective amounts of (a) at least one multiphotonphotosensitizer that is capable of simultaneously absorbing at least twophotons and that preferably has a two-photon absorption cross-sectiongreater than that of fluorescein; (b) optionally, at least one electrondonor compound different from the multiphoton photosensitizer andcapable of donating an electron to an electronic excited state of thephotosensitizer; and (c) at least one photoinitiator that is capable ofbeing photosensitized by accepting an electron from an electronicexcited state of the photosensitizer, resulting in the formation of atleast one free radical and/or acid.

Alternatively, the multiphoton photoinitiator system can be aone-component system that includes at least one photoinitiator.Photoinitiators useful as one-component multi-photon photoinitiatorsystems include acyl phosphine oxides (for example, those sold by Cibaunder the trade designation Irgacure 819, as well as 2,4,6 trimethylbenzoyl ethoxyphenyl phosphine oxide sold by BASF Corporation under thetrade designation Lucirin TPO-L) and stilbene derivatives withcovalently attached sulfonium salt moieties (for example, thosedescribed by W. Zhou et al. in Science 296, 1106 (2002)). Otherconventional ultraviolet (UV) photoinitiators such as benzil ketal canalso be utilized, although their multi-photon photoinitiationsensitivities will generally be relatively low.

Multiphoton photosensitizers suitable for use in the multiphotonphotoinitiator system of the resin 22 are those that are capable ofsimultaneously absorbing at least two photons when exposed to sufficientlight. Preferably, the photosensitizers have a two-photon absorptioncross-section greater than that of fluorescein (that is, greater thanthat of 3′,6′-dihydroxyspiro[isobenzofuran-1(3H),9′-(9H)xanthen]-3-one).Generally, the preferred cross-section can be greater than about50×10⁻⁵⁰ cm⁴ sec/photon, as measured by the method described by C. Xuand W. W. Webb in J. Opt. Soc. Am. B, 13, 481 (1996) (which isreferenced by Marder and Perry et al. in International Publication No.WO 98/21521 at page 85, lines 18-22).

More preferably, the two-photon absorption cross-section of thephotosensitizer is greater than about 1.5 times that of fluorescein (or,alternatively, greater than about 75×10⁻⁵⁰ cm⁴ sec/photon, as measuredby the above method); even more preferably, greater than about twicethat of fluorescein (or, alternatively, greater than about 100×10⁻⁵⁰ cm⁴sec/photon); most preferably, greater than about three times that offluorescein (or, alternatively, greater than about 150×10⁻⁵⁰ cm⁴sec/photon); and optimally, greater than about four times that offluorescein (or, alternatively, greater than about 200×10⁻⁵⁰ cm⁴sec/photon).

Preferably, the photosensitizer is soluble in the reactive species (ifthe reactive species is liquid) or is compatible with the reactivespecies and with any optional binders that are included in resin 22.Most preferably, the photosensitizer is also capable of sensitizing2-methyl-4,6-bis(trichloromethyl)-s-triazine under continuousirradiation in a wavelength range that overlaps the single photonabsorption spectrum of the photosensitizer (single photon absorptionconditions), using the test procedure described in U.S. Pat. No.3,729,313.

Electron donor compounds useful in the multiphoton photoinitiator systemof the photoreactive compositions are those compounds (other than thephotosensitizer itself) that are capable of donating an electron to anelectronic excited state of the photosensitizer. Such compounds may beused, optionally, to increase the multiphoton photosensitivity of thephotoinitiator system, thereby reducing the exposure required to effectphotoreaction of the photoreactive composition. The electron donorcompounds preferably have an oxidation potential that is greater thanzero and less than or equal to that of p-dimethoxybenzene. Preferably,the oxidation potential is between about 0.3 and 1 volt versus astandard saturated calomel electrode (“S.C.E.”).

The electron donor compound is also preferably soluble in the reactivespecies. Suitable donors are generally capable of increasing the speedof cure or the image density of a resin 22 upon exposure to a radiationbeam 26 of the desired wavelength.

Suitable photoinitiators (that is, electron acceptor compounds) for thereactive species of the photoreactive compositions are those that arecapable of being photosensitized by accepting an electron from anelectronic excited state of the multiphoton photosensitizer, which formsat least one free radical and/or acid. Such photoinitiators includeiodonium salts (for example, diaryliodonium salts), sulfonium salts (forexample, triarylsulfonium salts optionally substituted with alkyl oralkoxy groups, and optionally having 2,2′ oxy groups bridging adjacentaryl moieties), and the like, and mixtures thereof.

The photoinitiator is preferably soluble in the reactive species and ispreferably shelf-stable (that is, does not spontaneously promotereaction of the reactive species when dissolved therein in the presenceof the photosensitizer and the electron donor compound). Accordingly,selection of a particular photoinitiator can depend to some extent uponthe particular reactive species, photosensitizer, and electron donorcompound chosen, as described above. If the reactive species is capableof undergoing an acid-initiated chemical reaction, then thephotoinitiator is an onium salt (for example, an iodonium or sulfoniumsalt).

Further details regarding suitable resins for use in multiphotonphotopolymerization systems may be found, for example, in U.S. PatentApplication Ser. No. 60/979,229, and entitled “HIGHLY FUNCTIONALMULTIPHOTON CURABLE REACTIVE SPECIES,”.

The substrate 20, supported by the chuck 18, preferably supports resin22. While reference is made to a substrate 20 supporting resin 22throughout the present application, it is to be understood that in someembodiments, substrate 20 is not necessary, and resin 22 may be directlysupported by chuck 18. Substrate 20 may be formed of any suitablematerial or combination of materials sufficient to support resin 22.Substrate 20 may be formed by any conventional process, includinginjection molding, compression molding, embossing, extrusion embossing,polymerizing within a mold, stamping, casting, machining, etching,sintering, grinding, chemical and physical deposition, crystallization,curing (including single- and multi-photon curing), and the like. Insome embodiments, substrate 20 defines a substantially planar surfacefor supporting resin 22. In such embodiments, substrate 20 may include asilicon wafer, a glass plate, a machined substrate, or the like.

In yet other embodiments, substrate 20 may include a substantiallynon-planar surface. For example, substrate 20 may have a concave orconvex curvature along one or more than one axis. For example, substrate20 may be cylindrical, spherical, ellipsoidal, saddle-shaped, or thelike. In some embodiments, substrate 20 may be a precision roll, such asthose formed by diamond turning processes, polishing, or the like. Inthese embodiments, the surface of substrate 20 may be substantiallysmooth, or may include features, such as patterned features. In somepreferred embodiments, substrate 20 is substantially smooth whensubstrate 20 has a curvature.

Substrate 20 may include surface irregularities such as peaks orvalleys. In some embodiments, microstructured films, such as thoseformed from polyethylene terephthalate, polyimides, and the like, maymake suitable substrates. Additionally, in some embodiments substrate 20may have features including continuous or discontinuous patterns ofdepressions, protrusions, posts, channels, grooves, cavities, and thelike. The features may be formed by any conventional method including,for example, laser writing, chemical etching, molding, and the like.Structures such as, for example, microelectromechanical systems (MEMS),may be formed by multiphoton initiated polymerization on or in thefeatures on the substrate. Examples of adding structures to a featuremay be found, for example, in U.S. Patent Application Publication No.2003/0155667.

Substrate 20 may also include fiducial structures that enable theregistration of the position of substrate 20 in the x-y axis, as will bedescribed in further detail below. Fiducial structures may includecontinuous or non-continuous grooves, depressions, protrusions, or thelike.

Substrate 20 may be held relative to chuck 18 using any suitablemechanism. In one embodiment, substrate 20 is held substantiallystationary relative to chuck 18 with the aid of mechanical fasteners.Mechanical fasteners may include clips, screws, bolts, adhesives, andthe like. Mechanical fasteners are preferably located in a plurality oflocations with respect to substrate 20 to distribute the forces onsubstrate 20 and minimize or prevent unwanted deformation of substrate20.

In another embodiment, substrate 20 is held substantially stationaryrelative to chuck 18 with the aid of vacuum pressure. Vacuum pressuremay distribute the forces on substrate 20 more evenly than mechanicalfasteners, and may thus cause less unwanted deformation of substrate 20.

Chuck 18 defines a surface that supports substrate 20. Thus, in manycases, the configuration of chuck 18 is selected to complement theconfiguration of substrate 20. For example, in the embodiment shown inFIG. 1, chuck 18 defines a substantially planar surface 18A forsupporting substantially planar substrate 20. In other embodiments,substrate 20 may define a curved surface, in which case, chuck 18 may beshaped to support the curved surface of substrate 20. For example,substrate 20 may define a substantially cylindrical surface on whichresin 22 is supported; in which case, chuck 18 may be shaped to supportthe cylindrical substrate 20. Alternatively, the configuration ofsubstrate 20 may be selected to complement the configuration of chuck18. For example, chuck 18 may include a surface mounted on rollers, ormay include a lathe to rotate the substrate 20.

Chuck 18 may be fabricated from any one or more component materials, andmay be fabricated from one or more suitable materials that provide anaccurate, consistent location of the interface 24 of substrate 20 andresin 22 with a change in temperature. For example, chuck 18 may befabricated from one or more materials that exhibit a relatively lowcoefficient of thermal expansion (CTE). Suitable materials for chuck 18include, but are not limited to, granite, Perlumite, silicon carbide,and the like. A relatively low CTE is desirable for chuck 18 to maintainthe substantially planar surface 18A on which substrate 20 rests and toprovide a relatively small change of position of substrate 20 withrespect to beam 26 with a change in temperature.

In some embodiments, chuck 18 is movable along at least one of thex-axis, y-axis, and z-axis directions. Chuck 18 may be supported on anair bearing surface (ABS) to reduce friction between chuck 18 and stage16. Reducing friction between chuck 18 and stage 16 may help controlmodule 12 move chuck 18 along the x-axis and y-axis directions withgreater accuracy while requiring less energy. The ABS may be generatedwith any suitable source, such as compressed air, compressed nitrogen ora compressed inert gas.

Chuck 18 may be movable along at least one of the x-axis, y-axis, andz-axis direction with under power of a motor, for example. For example,in one preferred embodiment, a linear motor may be used to move thechuck 18 in a highly precise and accurate manner. In some embodiments,chuck 18 may also provide the capability to level substrate 20, forexample by providing independent z-axis adjustment at a plurality oflocations along chuck 18.

The stage 16 may also be fabricated from one or more suitable materials.In some embodiments, the stage 16 includes one or more materials with arelatively low CTE, such as, for example, granite. In other embodiments,the magnitude of the CTE is less important than the matching of CTEsthroughout exposure system 10. Matching the CTEs of the various modulesof exposure system 10 reduces the relative motion of the individualmodules with respect to each other due to different amounts of thermalexpansion or contraction, and may thus reduce the relative movement ofresin 22 and beam 26. In yet other embodiments, chuck 18 and stage 16may be passively or actively cooled using, for example, cooling fins,heat exchangers, or the like. Additionally, stage 16 may also besubstantially isolated from the structure that supports stage 16 (e.g.,a floor). Isolating stage 16 from the support structure may reduce theeffect of vibrations of the support structure on resin 22. Isolation ofstage 16 may be accomplished using materials such as polymer vibrationisolation pads, for example.

Control module 12 may change a position of chuck 18 in the x-, y-,and/or z-axes to change the location of focal point 28 of beam 26relative to resin 22. In some embodiments, however, at least one of thex-axis, y-axis, and z-axis positions of focal point 28 of beam 26relative to resin 22 is modified with the aid of components of opticalsystem 11.

Control module 12 generally controls optical system 11, and may alsoinclude one or more submodules. In one embodiment, control module 12includes a processor, such as a microprocessor, a controller, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA), discrete logiccircuitry, or the like. In some embodiments, the processor may implementsoftware, hardware, firmware or a combination thereof to control each ofmodules 32, 34, 36, 38, 82, 42, 46, and 110.

FIG. 2 is a block diagram of optical system 11 illustrating oneembodiment of a configuration of modules 32, 34, 36, 38, 82, 42, 46, and110, which together define an optical train. The order of the modulesshown in FIG. 2 is merely exemplary, and is to be understood to not belimiting in any manner. In other embodiments, for example, second beammonitor 42 and position detector 46 may be in a different order, whichmay depend upon the dimensions, geometry or other considerationsaffected by the space into which optical system 11 is incorporated. Thevarious modules 32, 34, 36, 38, 82, 42, 46, and 110 include both monitorsystems that measure a property of beam 26 and sub-systems capable ofmodifying the measured property of beam 26. For example, the measuredproperty may include at least one of power, pulse length, shape,wavelength, divergence, or position in a plane normal to the opticalaxis of the beam 26. Specific monitor systems and sub-systems capable ofmodifying a measured property of beam 26 will be discussed in furtherdetail below.

Light source 32 emits a beam of radiation pulses 26 of sufficientintensity to initiate at least partial cure of resin 22. In someembodiments, the beam 26 may include a relatively narrow wavelengthrange, such as the nominal wavelength plus or minus about 5 nm, and maybe said to be emitted substantially at a first wavelength. In someembodiments, such as those useful for multiphoton polymerization, thecenter wavelength of the emitted radiation pulses may be in the rangefrom about 400 nm to about 2000 nm, preferably from about 500 nm toabout 1000 nm, and more preferably from about 750 nm to about 850 nm.Light source 32 emits the radiation pulses along an optical axis 27defined by the path of the beam 26 from the light source 32 to the resin22. In embodiments in which optical system 11 is used in a multiphotonpolymerization process, light source 32 emits a beam 26 that hassufficient power to cause multiphoton absorption at a wavelengthappropriate for the multiphoton initiation system used in thephotoreactive composition of resin 22. Light source 32 emits a beam 26comprising the necessary peak power and intensity to initiate cure ofresin 22. In some embodiments, light source 32 may emit a beam includingan output pulse width of between about 1 femtosecond (fs) and about 10ps, such as about 100 fs. In some other embodiments, light source 32 mayemit a beam including an output pulse width of less than about 10 ns,preferably less than about 10 ps, and more preferably less than about100 fs. In some cases, a high pulse repetition rate may be desirable. Insome other embodiments, light source 32 may emit a beam including anoutput pulse repetition rate of greater than about 1 kHz or preferablygreater than about 50 MHz.

In one embodiment, light source 32 is a relatively low power, ultrashortlaser light, such as a pulsed femtosecond laser. As one example, lightsource 32 may include a Ti:sapphire laser, such as those available fromSpectra-Physics under the trade designation MaiTai, commerciallyavailable from Newport Corporation of Irvine, Calif., or may include afiber-based ultrafast laser.

In some embodiments, a voxel can be formed by a single laser pulse. Insome other embodiments, formation of a voxel requires two or morepulses. In other embodiments, the multiple pulses may initiate cure of aplurality of voxels. A “low pulse energy” laser beam 26 refers to a beamof radiation pulses 26 exhibiting an insufficient power to fully cure avolume of resin 22. Rather, with a low pulse energy beam 26, thesequential pulses are necessary to fully cure a volume within resin 22.

In another embodiment, light source 32 is a high power continuous wave(CW) laser that does not require multiple pulses to initiate a full cureof resin 22. However, in some cases, it may be desirable to minimize thepower of the laser beam 26 to minimize inadvertent heating of resin 22.Although it may be possible for the high power CW laser to initiate afull cure of a volume of resin 22 with a single pulse, the high power CWlaser may also be used to sequentially cure a voxel in a stepwisefashion, which in some cases can provide a more accurate cure profile.

In some embodiments, a relatively low pulse energy laser, which emits abeam 26 that is insufficient to initiate cure of a volume of resin 22without any optics, may be used in combination with optical elements.Focusing optics may increase the intensity of the beam 26 outputted fromlight source 32, thereby enabling the beam 26 emitted by low pulseenergy light source 32 to cure resin 22. If desired, focusing optics mayalso be designed to decrease the intensity of the beam 26 outputted bylight source 32. The combination of optical elements that are used toachieve the desired intensity beam 26 from light source 32 may bereferred to as “pupil function synthesis.” As described in furtherdetail below, pupil function synthesis may focus the beam 26, impart aparticular shape to the beam 26 at focal point 28, which may bedesirable for controlling the size of the voxel formed within resin 22,or change the shape of the beam 26.

Light source 32 may emit a beam 26 having an inadvertently fluctuatingpower or trajectory. The power fluctuations may result in unstablepositioning of focal point 28 of beam 26, which may adversely affect theability of optical system 11 to precisely and accurately control theposition of focal point 28 relative to resin 22. High or low frequencyvibrations of one or more components of optical system 11 may alsoadversely affect the positioning of focal point 28. For example,vibrations from an air handling unit (e.g., for a heating, ventilationor air conditioning system) for the building in which system 10 islocated may cause vibrations.

A first example monitor may include a first beam monitor 34 and/or asecond beam monitor 42. Because of the high degree of control desiredover the position of focal point 28 of beam 26, the position of the beam26 may be sampled and controlled at one or more locations within opticalsystem 11. At each of the locations, a beam monitor may be provided tomeasure at least one characteristic of the beam 26 and output a signalbased on the at least one characteristic to a device, such as controlmodule 12, that can control optical elements that affect the position,power and/or shape of the beam 26. In some embodiments, such as theembodiment illustrated in FIG. 2, optical system 11 includes a firstbeam monitor 34 and a second beam monitor 42 to provide positionmonitoring and correction of a first characteristic of the beam 26 attwo locations in the optical system 11. Each of the first and secondbeam monitors 34, 42 may include a position sensing detector (PSD) 62, adigital camera 64, a beam steering module 66, and a control module 68,as shown in FIG. 3.

Control module 68, like control module 12 of exposure system 10, mayinclude a processor, such as a microprocessor, DSP, an ASIC, a FPGA,discrete logic circuitry, or the like. The processor may implementsoftware, hardware, firmware or a combination thereof to control each ofdetector 62, digital camera 64, and beam steering module 66. Althoughthe embodiment of beam monitors 34, 42 shown in FIG. 3 includes controlmodule 68 to control position sensing detector 62, digital camera 64,and beam steering module 66, in other embodiments control module 12 ofexposure system 10 may provide the necessary control. Alternatively,control modules 12, 68 may be used in combination with each other.

To properly correct the position of focal point 28, first beam monitor34 and second beam monitor 42 include a PSD 62 to measure the positionof beam 26 at a relatively high speed. In some embodiments, the PSD 62includes a quadrant detector, which includes four silicon chips thatindicate the position of the beam 26 in the x-y plane (the plane normalto the optical axis 27) based on the voltage outputted by the siliconchips in each quadrant. The PSD 62 a signal to beam monitor controller68, which uses the signal to control beam steering module 66.

The beam monitors 34, 42 may include a digital camera 64 in addition toa PSD 62 to provide beam 26 position information (in the plane normal tothe optical axis 27) than the PSD 62. Digital camera 64 may also provideinformation relating to the size, shape, and/or power of the beam 26.Digital camera 64 may be any suitable camera that is sensitive to thewavelength of beam 26, such as, for example, a CCD or CMOS camera.Digital camera 64 may be used to determine information about beam 26that is not critical to the feedback loop of the beam monitors 34, 42.For example, digital camera 64 may be useful for providing informationthat indicates the shape, size, and/or intensity regions of beam 26. Ifbeam 26 does not provide the desired results (e.g., resin 22 is notcured as desired), feedback from digital camera 64 may be used toisolate the source of the problem.

Digital camera 64 may also be used in closed-loop feedback to change oneor more characteristics of the beam 26. For example, the size or shapeof the beam 26 monitored by digital camera 64 in each of first beammonitor 34 and second beam monitor 42 may be used by the divergencemonitor 36 to determine whether an undesired divergence or astigmatismis present in beam 26. The divergence monitor 36 may then use thisinformation to instruct first divergence modulator 38 to provide acorrection to beam 26 to remove the unwanted divergence or astigmatism,as will be described in further detail below. In some embodiments,however, digital camera 64 may not be actively input into a controlsystem, but the information provided by digital camera 64 may instead beused for later analysis of the operation of optical system 11.

Control module 68 receives beam 26 position information from positionsensing detector 62 and digital camera 64, and controls a sub-systemcapably of modifying the position of beam 26, such as, for example, beamsteering module 66 to reposition beam 26 based on the positioninformation. Beam steering module 66 may include any optical elementsuseful for repositioning or redirecting beam 26, including, for example,lenses, mirrors, and the like. In one embodiment, beam steering module66 includes at least one piezoelectric-actuated mirror that makesrelatively high-speed corrections to the position of beam 26. Thepiezoelectric-actuated mirror may make corrections along one or two axesto reposition beam 26 substantially within the plane normal to theoptical axis 27. As another example, beam steering module 66 may includetwo piezoelectric-actuated mirrors. The first of the two mirrors maymake slow, but large magnitude movements to compensate for drift in beam26 while the second mirror performs relatively faster corrections ofsmall magnitudes to cancel out high frequency vibrations from opticalsystem components. In other embodiments, any suitable number of mirrorsmay be used, or the mirror may be actuated by another system, such as agalvanometer.

In an alternative embodiment, the first and second beam monitors 34, 42may be used to introduce a controlled amount of noise into the positionof beam 26. This controlled amount of noise may serve to smooth theedges or surfaces of an at least partially cured structure formed inresin 22.

Light source 32 may emit a beam 26 that includes an astigmatism thatresults in a non-circular shape in a plane normal to the optical axis27, as described briefly above. Light source 32 may also emit a beam 26that include some amount of divergence, also described briefly above.Additionally, both the astigmatism and divergence of the beam 26 asemitted by light source 32 may vary over time. Accordingly, the opticalsystem 11 may include a monitor system for monitoring astigmatism anddivergence of beam 26. The divergence monitor 36 may monitor both theastigmatism and the divergence of beam 26. While divergence monitor 36is illustrated in FIG. 2 as following the first beam monitor 34,divergence monitor 36 may be located at any point in the optical system11. Additionally, in some embodiments, divergence monitor 36 may utilizethe outputs of first and second beam monitors 34, 42 to determine anyastigmatism or divergence present in beam 26.

In embodiments where the divergence monitor 36 is a discrete module,divergence monitor 36 may sample a small portion of beam 26 using, forexample, a beam splitter, a beam sampling mirror, or the like whiletransmitting the majority of beam 26 through to the rest of opticalsystem 11. In one embodiment, the small portion of beam 26 may bedirected through an amplitude beam splitter that splits the beam 26 toform two beamlets. One of the beamlets travels a short path to acamera-based two-dimensional (2D) sensor, such as a CCD camera, whilethe other beamlet travels a longer path to the 2D sensor. If the twobeamlets are not the same size as measured by the 2D sensor, therelative difference in size (e.g., a width or area) of the two beamletsdetermines amount of divergence of beam 26.

In another embodiment, divergence monitor 36 monitors the divergence ofbeam 26 using an interferometric approach. In the interferometricapproach, the beam 26 interferes with itself, producing an equal opticalpath lateral shear (with a slight wedge) or rotational shear. Thefringes produced allow for determination of the degree of collimation ina compact and simple configuration.

The divergence monitor 36 (e.g. a CCD camera) also measures a shape ofthe beam 26 in a plane normal to the optical axis 27. The shape of beam26 indicates the presence or absence of astigmatism or ellipticitypresent in beam 26, which may result in a focal point 28 having anelliptical or other non-spherical shape. Depending on the intendedapplication, astigmatism may or may not be desirable. For example,purposefully maintaining or introducing astigmatism into beam 26 mayresult in an elliptically shaped (or other non-circular shaped) beam 26in a plane normal to the optical axis 27, which may more effectively orefficiently initiate cure of a selected voxel.

In other embodiments, divergence monitor 36 may use the output of thedigital camera 64 of each of first and second beam monitor 34, 42 todetermine a divergence and astigmatism of beam 26. For example, eachdigital camera 64 may monitor a size and shape of the beam 26 in a planenormal to the optical axis 27. Because each beam monitor 34, 42, andthus each digital camera 64, monitors a characteristic of the beam 26 ata different location within optical system 11, any change in the size orshape of the beam 26 as the beam 26 passes through optical system 11 maybe detected by comparing the output of digital camera 64 of first beammonitor 34 with the output of digital camera 64 of second beam monitor42. This comparison may be performed by divergence monitor 36, bycontrol module 12, or by another control module, such as control module68 of one of the beam monitors 34, 42.

The divergence and shape of the beam 26 as measured by divergencemonitor 36 may be output to control module 12 or another control module(such as, for example, a control module dedicated to divergence monitor36 and first divergence modulator 38) to determine whether anyastigmatism or divergence correction is necessary. Control module 12controls a sub-system capable of modifying a divergence or shape of beam26, such as, for example, first divergence modulator 38 to provide anydivergence or astigmatism correction necessary to beam 26. The firstdivergence modulator 38 may include two elements each having an opticalpower, such as, for example, two equal positive lenses 72, 76 spacedapart a distance of about two focal lengths F for approximately 1:1expansion of the input beam 26, as shown in FIG. 4. Lens 72 may bemounted on a rotational stage that controls the rotational position oflens 72 to control astigmatism correction in response to any astigmatismmeasured by divergence monitor 36. Lens 74 may be mounted on a linearstage for controlling the position of lens 74 in the x-axis of FIG. 4.The linear stage may move lens 76 in the negative x-axis direction (tothe left in FIG. 4) to increase the divergence of beam 26, or more lens76 in the positive x-axis direction to decrease the divergence of beam26 (i.e., increase the convergence of beam 26).

Optical system 11 further includes an exposure control module 82, whichincludes at least one monitor system and at least one sub-system capableof modifying a property of beam 26 to control exposure of resin 22 tobeam 26. For example, in embodiment illustrated in FIG. 5, exposurecontrol module 82 includes a control module 84, a safety shutter 86, apower meter 88, a power control 40 and a high speed shutter 44. Powercontrol 40 controls the power of beam 26, and high speed shutter 44initiates and terminates the exposure of resin 22 to beam 26 toselectively initiate cure of portions of resin 22 and create discreet 3Dfeatures or structures. In some embodiments, power control 40 and highspeed shutter system 44 may include separate modules. As previouslydescribed, the process of curing resin 22 to form a voxel issubstantially nonlinear, and any deviation from the desired laser powerduring the exposure process may create errors. Thus, it is importantthat power control 40 maintains the power of radiation beam 26 at adesired level or within a certain range of the desired level.

It is also preferable that both the power control 40 and high speedshutter 44 respond substantially as quickly or more quickly that anyother component of optical system 11. For example, the first and secondgalvanometers 50, 52 are typically the fastest components in the opticalsystem 11, so the power control 40 and high speed shutter 44 preferablyrespond at a speed substantially equal to or greater than the speed ofthe first and second galvanometers 50, 52.

In some embodiments, exposure control module 82 includes a safetyshutter 86. Safety shutter 86 may be useful for providing controlledstart-up and shut-down of optical system 11. As an example, safetyshutter 86 may block beam 26 from exposing resin 22 while light source32 is warming up, and may be closed while the remaining components ofoptical system 11 are shut down. In some types of laser beams, the laserwarms-up prior to reaching a steady level of power. For example, theSpectra-Physics MaiTai laser may take between about five minutes toabout 30 minutes to stabilize to a desired level for use in multiphotoncuring processes. However, in some cases, safety shutter 86 may blockbeam 26 for a time sufficient to provide a beam 26 with a desired levelof stability. During the warm-up period, beam 26 may undergofluctuations in power and stability of beam trajectory (e.g., thepredictability of the location of the focal point 28). Control module84, or control module 12 of exposure system 10, may control safetyshutter 86 to block beam 26 during the warm-up period, as well as atother times during which it is undesirable for the beam 26 to exposeresin 22. For example, safety shutter 86 may be used as an emergencyshut-off of optical system 11, in addition to or instead of turning offlight source 32. In some embodiments, safety shutter 86 may also blockbeam 26 during calibration of beam 26.

Exposure control module 82 also includes high speed shutter system 44that initiates and terminates exposure of beam 26 after beam 26 issubstantially stabilized and resin 22 is in a desired position relativeto focal point 28 of beam 26. Control module 84 within exposure controlmodule 82 may control the shutter system. A “high” speed shutter system44 may generally be any shutter system that may turn the beam 26 on oroff at a speed above about one switch between an on/off stage per 1millisecond. More preferably the high speed shutter system may turn thebeam 26 on or off at a speed above 1 microsecond, and most preferably aspeed greater than about 50 nanoseconds (50 ns), such as a speed ofabout one on/off cycle in about 20 ns.

In one embodiment, the high speed shutter system 54 includes a Pockelscell and a polarizer. In the Pockels cell, voltage is applied to acrystal(s) that may alter the polarization properties of a passing beam26. In one type of high speed shutter, the Pockels cell is combined witha polarizer. The Pockels cell may be switched between a no opticalrotation position (0°) and a generally 90° rotation to define a shutterthan opens or closes in nanoseconds. In addition, the Pockels cell andpolarizer combination may be rotated to a position between 0° and 90° tochange the power of beam 26 before the resin 22 is exposed.

In another embodiment, high speed shutter system 44 includes anacousto-optic modulator (AOM), which uses the acousto-optic effect todiffract and shift the frequency of light using sound waves, such asradio-frequency sound waves. In one type of AOM, a piezoelectrictransducer is attached to a material such as glass, and an oscillatingelectric signal vibrates the transducer, which creates sound waves inthe glass. The sound waves change the index of refraction, whichdisperses the incoming beam 26 from light source 32. In some cases,however, such as when light source 32 incorporates a femtosecond laser,the optical dispersion of the beam 26 within the AOM may affect theoptical precision of beam 26.

In yet other embodiments, high speed shutter system 54 may includemechanical switching devices, such as one or more mechanical shutters, avariable filter or etalon. The high speed shutter system 54 may alsoinclude a half-wave plate and polarizing beam splitter or a half-waveplate and polarizer, which will be described in further detail belowwith respect to power control 40. The Pockels cell, AOM, mechanicalswitching devices, and other high speed shutter systems may be usedalone or in combination with each other.

Power meter 88 may monitor the power of beam 26 at a desired locationwithin optical system 11. Additionally, in some embodiments, opticalsystem 11 may include more than one power meter 88 to monitor the powerof beam 26 in a plurality of locations within optical system 11. Powermeter 88 may comprise, for example, a multimeter, which includes asilicon chip that outputs a voltage indicative of power. In somepreferred embodiments, power meter 88 includes a National Institute ofStandards and Technology (NIST)-traceable power meter.

In some embodiments, a beam sampler may reflect a portion of the beam26. This reflected portion of beam 26 may be monitored by the powermeter 88 to determine the power of the entire beam 26. Although only aportion of beam 26 is input into the power meter 88, power meter 88 orcontrol module 84 may use an appropriate algorithm to estimate the powerof the entire beam 26 based on a power measurement of the portion. Basedon the power measurement, power meter 88 may provide feedback to controlmodule 84, which may then adjust the power of beam 26 as necessary. Forexample, the power of beam 26 may be adjusted at light source 32 or bypower control 40. In other embodiments, as described below, the powercontrol 40 may include a beam splitter that directs a portion of beam 26to power meter 88, while transmitting the remaining portion of beam 26through the rest of the optical system 11.

Power control 40 may help correct any power variations in beam 26, orcontrol the power of beam 26 to a desired level, prior to beam 26exposing resin 22. With some radiation sources used by light source 32,even after beam 26 achieves a substantial equilibrium, beam 26 mayexhibit variation in the output power. For example, the power variationmay vary within a range of plus or minus one percent of the desiredpower output for beam 26. Such power variation may be undesirable whenbeam 26 is used to pattern relatively small-scale features, e.g.,nanometer scale features, within resin 22.

Accordingly, power control 40 may adjust the power of beam 26 to thedesired level. In some embodiments, the power control 40 includes ahalf-wave plate (HWP) and polarizing beam splitter (PBS) or a HWP and apolarizer to attenuate the light from light source 32. In someembodiments, power control 40 attenuates the light from light source 32when light source 32 outputs a beam 26 that has a power greater thanthat desired to at least partially cure resin 22. Reducing the power ofbeam 26 helps to reduce the size of an at least partially cured voxelcreated by the exposure of a volume of resin 22 to focal point 28 ofbeam 26.

In some embodiments, incoming light (e.g., beam 26) directed at the PBSmay be split into at least two portions by the PBS, where a firstportion is directed by the PBS into the power meter 88, which mayestimate the power of beam 26 based on the power of the first portion ofbeam 26, while another portion of beam 26 is directed by the PBS throughthe remaining portion of the optical system 11 towards the focal plane14.

In one embodiment, as shown in FIG. 6, the HWP 92 is mounted forrotational movement, and a high-speed galvanometer motor rotates the HWP92 under the control of control module 84 or another appropriate controlmodule, such as control module 12 of fabrication system 10. In oneembodiment, the HWP 92 may be rotated about 45° in each of the clockwiseand counterclockwise directions about a central axis 91, for a totalrotation of about 90°. As the HWP 92 is rotated a polarization componentof the beam 26 is rotated. The beam 26 exits the HWP 92 and encounters aPBS 93. Depending on the polarization properties of beam 26, differentamounts of beam 26 may be transmitted through PBS 93, thus changing thepower of the beam 26. In some preferred embodiments, the portion of beam26 reflected by the PBS 93 continues through the rest of optical system11 and the transmitted portion of beam 26 is not used.

The dependence of the power of beam 26 on the angle of HWP 92 may beexperimentally determined and a corresponding curve 101 of power versusangle may be created, as shown in FIG. 7. While one type of potentialcurve 101 is shown in FIG. 7, other curves may be possible, such as, forexample, linear curves, exponential curves, and the like. Theexperimentally-derived curve may be programmed into software and used tocontrol the power of beam 26 by the rotation of HWP 92.

In general, the HWP 92 helps achieve a relatively high-speed powercontrol such that the power of beam 26 for the voxel creation processmay be changed substantially in real-time while creating one or morevoxel within resin 22. The relatively high-speed power control enablesthe volume of an at least partially cured voxel to be variedsubstantially in real-time, as well.

For a given resin 22, voxel size may generally be thought of as afunction of the amount of energy absorbed by a volume of resin 22. As asimplification, the total amount of energy absorbed by a volume of resin22 may be approximately proportional to the amount of time a volume ofresin 66 is exposed to focal point 28 of beam 26 multiplied by the powerof beam 26. The relationship between the power of beam 26, scanningvelocity of beam 26 (and thus time of exposure of a volume of resin 22),and the voxel size may be quite complex and may be linear or non-linearat different power/velocity combinations.

By experimentally determining the relationship between power/scanvelocity and voxel size, a correlation may be provided to control module84, or another suitable control module, that enables the control ofoptical system 11 to produce a voxel of a desired volume within resin 22by varying the power of beam 26, the scan velocity of beam 26, or both.For example, to maintain a substantially constant voxel size when thescan velocity of beam 26 is decreased, the power of beam 26 may also bedecreased by a necessary amount (e.g., an experimentally determinedamount).

Alternatively, the combination of power and scan velocity of beam 26 maybe chosen to provide a desired voxel size change. As one example,increasing the power at a given scan rate may result in a larger voxelsize, which may be desirable for quickly curing a large volume of resin22 with features of a limited resolution. In this example, the power maybe lowered (while still maintaining an intensity above a thresholdintensity) to create a smaller voxel, and thus higher resolutionfeatures, either before or after the curing of the large volume withlimited resolution.

In another embodiment, a Pockels cell may also be used to providereal-time power control. For example, applying a prescribed voltage to aPockels cell may result in a predetermined alteration of a polarizationproperty of beam 26 passing through the Pockels cell. In this way, aPockels cell may replace the HWP 92 and, in combination with a PBS 93,provide real-time power control of beam 26.

In yet other embodiments, the power control 40 and high speed shutter 44may include the same components, such as a HWP 92 and PBS 93 thatfunction as both a power control 40 and a high speed shutter 44. Then,the power may be controlled by controlling the rotation of HWP 92, andthe high speed shutter 44 may be activate by rotating the HWP 92 topolarization orientation orthogonal to the polarizer 93 orientation.

The control module 84, or another control module, may control powercontrol 40 to attenuate beam 26 and provide a beam 26 of the desiredpower based on the output of power meter 88, or another power meter,such as power detector 185, power detector 212, or power detector 213.

In other embodiments, exposure control module 82 may include other powerand energy monitoring devices in addition to or instead of power meter88. Furthermore, other power and energy monitoring devices may beincorporated into optical system 11 at specific steps or intervals andat various locations to set the desired power level or track the powerlevels or time with regards to specific optical components.

Optical system 11 may further include another monitor system, which isreferred to hereinafter as a position detector 46. Position detector 46monitors the position of the focal point 28 of beam 26 along the opticalaxis 27. Specifically, position detector 46 monitors the position of thefocal point 28 with respect to the interface 24 between substrate 20 andresin 22. Locating and tracking the position of focal point 28 withrespect to interface 24 is important in many embodiments, becausevariations in the interface 24 may be a substantial portion of theheight of the structures formed in resin 22. Additionally, whenstructures are formed in resin 22 and not attached to the surface ofsubstrate 20, any subsequent processing, such as solvent development toremove any unexposed portions of resin 22, may remove the structuresfrom substrate 20.

Position detector 46 may include a wide range of detectors, includingfor example, capacitive sensors, interferometers, confocal sensors, andthe like. A confocal sensor is generally preferred, such as the confocalsensor described in U.S. Patent Application Ser. No. 60/752,529,entitled, “METHOD AND APPARATUS FOR PROCESSING MULTIPHOTON CURABLEPHOTOREACTIVE COMPOSITIONS.”. A confocal sensor is a diagnostic devicethat detects the interface 24 between resin 22 and substrate 20 wheninterface 24 is located at or near the focus of the optical system 11.The focal point 28 of the optical system 11 is conjugate to a pinholethat only allows light that is retro-reflected from interface 24 at theoptical system 11 focus to pass through the pinhole. All other pointsare out of focus and are not detected. This apparatus accurately locatesthe interface 24 of resin 22 and substrate 20. Typically, optics and ahigh speed detector are located behind the pinhole. In some embodiments,the pinhole is replaced with a single- or multi-mode fiber, whichbehaves like a pinhole, except the light is guided to the high speeddetector.

However, it is difficult to determine what side of interface 24 thefocal point 28 is on if it is not located at interface 24. Thus, achromatic confocal sensor may be utilized, such as those described inU.S. Patent Application Ser. No. 60/979,240, and entitled “CHROMATICCONFOCAL SENSOR.” A chromatic confocal sensor may provide an improvedrange of detection of the focal point 28 with respect to interface 24along the optical axis 27.

The confocal sensor may utilize either beam 26 or another interrogatorbeam, which preferably includes the wavelength or wavelength range ofbeam 26, to measure the location of the focal plane with respect tointerface 24. When a confocal sensor is utilized to measure the locationof the focal plane, the optical system 11 includes optical componentsthat collect at least a portion of the beam (either beam 26 or aseparate interrogator beam) that is retroreflected off of interface 24and direct that portion to a spectrometer. The optical components mayinclude, for example a polarizing beam splitter and an optical relay.The spectrometer then monitors the intensity, and optionally, thewavelength, of the retroreflected beam and uses this information todetermine the location of focal point 28 with respect to interface 24.If an interrogator beam is utilized, it is preferable that theinterrogator beam is directed through the objective lens 114 andincludes the wavelength of beam 26 so that the focal point of theinterrogator beam and beam 26 is substantially the same, thussimplifying the location of focal point 28 with respect to interface 24.

The position detector 46 may also be used to locate the substrate 20 inthe plane substantially perpendicular to the optical axis 27 (the x-yplane in FIG. 1). As described above, the substrate 20 may includefiducial structures, such as grooves, depressions, protrusions, and thelike. Because position detector 46, such as a confocal sensor, locatesthe focal plane with respect to the interface 24 of substrate 20 andresin 22, depressions or protrusions, if present, are easily located bya change in the signal output by the position detector. When thelocation of the depressions or protrusions with respect to the substrate20 (in the x-y plane) is known, the location of the focal point 28 withrespect to the substrate 20 in the x-y plane may accordingly bedetermined.

FIG. 8 is a block diagram of optical scanning module 110, which includessub-systems capable of modifying the position of beam 26, such as, forexample, control module 112, objective lens 114, second divergencemodulator 48, first and second galvanometers 50, 52, and optical relayassembly 116. Optical scanning module 110 directs beam 26 toward imageplane 14 and focuses radiation onto image plane 14 with substantiallysubmicron precision. In various embodiments, optical scanning module 110directs and focuses beam 26 in one, two or three dimensions.

Control module 112, like control module 12 of exposure system 10, mayinclude a processor, such as a microprocessor, DSP, an ASIC, a FPGA,discrete logic circuitry, or the like. The processor may implementsoftware, hardware, firmware or a combination thereof to controlobjective lens 114, divergence modulator 48, and first and secondgalvanometers 50, 52. Although the embodiment of optical scanning module110 shown in FIG. 8 includes control module 112, in other embodiments,control module 12 of exposure system 10 may provide the necessarycontrol of objective lens 114, divergence modulator 48, and first andsecond galvanometers 50, 52. Alternatively, control modules 12, 112 maybe used in combination with each other.

One sub-system capable of modifying the position of beam 26 includesobjective lens 114, which focuses beam 26. Objective lens 114 comprisesa numerical aperture (NA) that is sufficient (in combination with beam26 as output by light source 32) to achieve the intensity necessary tocure resin 22, and, accordingly, the NA of objective lens 114 may differdepending upon the type of resin 22, as well as the size of the voxel tobe defined in the at least partially cured resin 22. In one embodiment,objective lens 114 comprises a high NA objective lens, such as an NA ina range of about 1.0 to about 1.8. An “objective” lens may also bereferred to as an “objective,” a “positive” lens or a “focusing” lens.In some embodiments, objective lens 114 may include an immersionobjective, such as an oil immersion objective, or an index matchingfluid. The immersion objective may be included to prevent sphericalaberration from occurring in beam 26 due to the refractive indexmismatch of objective lens 114 and a dry air objective, for example.Objective lens 114 focuses focal spot 26 of beam 26 tightly into layerof resin 22 to achieve a threshold intensity to initiate cure of regionsof layer of resin 22 that are exposed to the portions of beam 26exhibiting at least the necessary threshold intensity (e.g., focal point28). In one embodiment, objective lens 114 is a Nikon CFI Plan Fluoro20× objective lens, which is available from Nikon Corporation of Tokyo,Japan. The Nikon 20× Multi Immersion Objective has a numeral aperture of0.75 and a field of view of 1.1 millimeters (mm).

The front focal plane (i.e., the focal plane closest to resin 22) ofobjective lens 114 may be selected to align with various other opticalelements of optical system 11, such as mirrors, a focus of an opticalrelay, or image plane 14. If a collimated beam pivots about the frontfocal plane in two dimensions, the focused beam will effectively “scan”as a telecentric imaging system across image plane 14 in two dimensions.In one embodiment, optical scanning module 110 is configured to pivot acollimated beam about the front focal plane of the objective lens 114,so as to achieve x-axis and y-axis positioning of beam 26.

Optical scanning module 110 further includes first and secondgalvanometers 50, 52, and one or more optical relay assembly 116, whichincludes one or more optical elements that relay an image to a virtuallocation, such as image plane 14. First and second galvanometers 50, 52,either alone or in combination with an optical relay assembly 116,comprise a sub-system capable of modifying the position of beam 26 in atleast one direction in a plane normal to the optical axis. In oneembodiment, the galvanometers 50, 52 may comprise mirrors mounted on agalvanometer that pivots or rotates the mirror in one or two dimensions.The image produced by optical relay assembly 116 may be considered an“internal” image. Optical relay assembly 116 may be useful in cases inwhich it is desirable to scan beam 26 in an x-axis, y-axis or z-axisdirection, but the scanner (e.g., objective lens 114) does notphysically fit within the desired space. Optical system 11 may bearranged such that the scanner may be placed in any suitable location,while maintaining the ability to scan beam 26 by relaying a scannedlocation of beam 26 to the desired location (e.g., image plane 14).While it is still possible for the scanner to scan beam 26 in one ormore directions without the aid of optical relay assembly 116, it may beundesirable to do so from a relatively far distance because it mayresult in a curved image plane or aberrations in beam 26, which may bedisadvantageous.

A schematic ray diagram of one embodiment of a basic optical relay 120is shown in FIG. 9. In some embodiments, optical relay 120 may beincorporated into optical relay assembly 116 of optical scanning module110. In FIG. 9, optical relay 120 includes object 122, first lens 124A,second lens 124B that is substantially identical to lens 124A, andobject 126. Objects 122 and 126 are images of objects. Lenses 124A and124B each have a focal length F, and, as a result, objects 122 and 126are separated by about four focal lengths F₁. Furthermore, becauselenses 124A and 124B are substantially identical, optical relay assembly116 provides a 1:1 magnification, such that objects 122 and 126 aresubstantially identical in size.

In other embodiments, other magnification ratios are possible.Furthermore, in other embodiments, other types of optical relaysincluding a fewer or greater number of optical elements may be employedby optical scanning module 110. For example, in some embodiments,optical relay assembly 116 may be utilized with one or moregalvanometers 50, 52 that tilt at various angles to scan beam 26 in one,two or three dimensions. A schematic ray diagram of one embodiment of asystem 130 including two optical relays 134 and 140 and twogalvanometers 50, 52 is shown in FIG. 10A.

System 130 includes galvanometer 50, optical relay 134 that includeslenses 136A and 136B, galvanometer 52, and optical relay 140 thatincludes lenses 242A and 242B. System 130 may be included within opticalrelay assembly 116 of FIG. 8. System 130 may be used to scan acollimated beam 26, or any other type of beam 26, within at least onedimension. In the embodiment shown in FIG. 10A, system 130 is configuredto scan collimated beam 26 in the x-axis and y-axis directions(orthogonal x-z axes are show in FIG. 10A; the y-axis is oriented normalto the plane of FIG. 10A).

As FIG. 10A illustrates, beam 26 is directed at galvanometer 50, whichscans beam 26 in a substantially perpendicular direction, toward opticalrelay 134. After beam 26 passes through lenses 136A and 136B of opticalrelay 134, beam 26 projects onto galvanometer 52, which scans beam 26 ina substantially perpendicular direction, toward optical relay 140 andthrough lenses 142A and 142B of optical relay 140. Galvanometer 52 ispositioned at the internal image of first optical relay 134, and in thisway, the internal image of first optical relay 134 is also the object ofsecond optical relay 140.

In general, control module 112 of optical scanning module 110 maycontrol the orientation of first and second galvanometers 50, 52 to scanbeam 26 in the x-axis and y-axis directions. The relative position beam26 in the x-axis and y-axis directions may be mapped to the relativeposition of galvanometers 50, 52. Thus, a given position of each ofgalvanometers 50, 52 may correspond to a location of beam 26 in thex-axis and y-axis of the image plane 14. Control module 112 may controlthe position of each of first and second galvanometers 50, 52 based onthe signals output by first and second beam monitors 34, 42, or based onchuck mounted PSD 214.

It has been found that in some embodiments, first and secondgalvanometers 50, 52 provide relatively fast and accurate scanning ofbeam 26, compared to some piezoelectric scanners and acousto-opticscanners. Fast scanning of beam 26 may help increase the speed withwhich structures are formed within resin 22. In one embodiment, firstand second galvanometers 50, 52 may include dielectric coated berylliummirrors rotated by a galvanometer. In some embodiments, it may bedesirable that the speed at which beam 26 is scanned by galvanometers50, 52 is less than the speed at which power control 40 adjusts thepower of beam 26.

Objective lens 114 may be positioned such that its back focal plane isat the internal image of second relay 140, such that a focused beam iscreated at image plane 14. For example, as shown in FIG. 10B, objectivelens 114 in housing 144 is positioned downstream of lens 142B of secondoptical relay 140, such that the internal image of beam 26 resultingfrom second optical relay 140 is focused through objective lens 114.Objective lens 114 focuses beam 26 onto image plane 14, and beam 26 maybe scanned in at least two dimensions, such as along the x-axisdirection and y-axis direction (substantially perpendicular to the planeof the image shown in FIG. 10B).

While optical relay assembly 116 and first and second galvanometers 50,52 scans beam 26 in substantially along the x-y axes relative to imageplane 14, optical scanning module 110 may further comprise a at leastone sub-system capable of modifying the position of focal point 28 inthe z-axis (orthogonal x-z axes are shown in FIG. 4), including, forexample, second divergence modulator 48, objective lens 114, and chuck18. Scanning focal point 28 of beam 26 substantially along the z-axismay help to achieve voxel positioning within resin 22 substantiallyalong the optical axis 27 (the z-axis if FIG. 1). Although threetechniques for scanning focal point 28 substantially along a z-axisdirection are described below, any suitable technique may be employed.For example, in different embodiments, the techniques for scanning focalpoint 28 substantially along the optical axis 27 may employ mechanicaldevices, optical devices or a combination thereof.

In one embodiment, a motor or piezo-electric device translates objectivelens 114 substantially along the z-axis direction to scan focal point 28substantially along the optical axis 27. In some cases, scanningobjective lens 114 in the optical axis 27 may affect the accuracy ofbeam 26 positioning in the x-y plane. Additionally, in some embodiments,a piezo-electric device provides a limited range of the position offocal point 28 in the optical axis 27, such as, for example, about 400nm. However, translating objective lens 114 to scan focal point 28 ofbeam 26 substantially along the optical axis 27 may provide a relativelyaccurate positioning of beam 26 compared to other beam scanningtechniques.

In another embodiment, rather than scanning focal point 28 of beam 26substantially along the optical axis 27, exposure system 10 may includea mechanical assembly to move chuck 18 substantially along the z-axisdirection. Moving chuck 18 to change the optical axis 27 positioning offocal point 28 within resin 22 enables optical system 11 to remainsubstantially in place. However, resin 22, substrate 20, and chuck 28may constitute a relatively large mass to move, and therefore, movingchuck 18 may be a relatively slow process, which may decrease thethroughput of exposure system 10. That is, in some cases, the weight ofresin 22, substrate 20, and chuck 18 may adversely impact the speed atwhich exposure system 10 creates voxels within resin 22.

FIG. 11 is a schematic illustration of second divergence modulator 48,which may be used in a technique for scanning beam 26 substantiallyalong the optical axis 27. Modulator 48 alters a divergence of beam 26before beam 26 enters objective 54. Divergence modulator 48 may be, forexample, an afocal telescope, such as, for example, a Kepleriantelescope.

Divergence modulator 48 includes focusing lens assembly 152 andcollimation optics 156. Focusing lens assembly 152 is configured to movealong the x-axis (orthogonal x-z axes are shown in FIG. 11). As focusinglens 152 moves along the x-axis, the internal focus of beam 26 passesthrough the front focal plane 154 of collimation optics 156. When theinternal focal point aligns with the front focal plane 154 ofcollimation optics 156, as is illustrated in FIG. 11, beam 26 emergesfrom collimation optics 156 collimated. When the internal focal point islocated on the left side of front focal plane 154, the beam 26 isconvergent as it emerges from divergence modulator 48, and beam 26 ismore convergent when the internal focal point is further to the left offocal plane 154. Conversely, if the internal focal point is located tothe right of focal plane 154, beam 26 emerges as a diverging wavefront.

An optical relay, such as optical relay 120 of FIG. 9 (not shown in FIG.11) may reproduce the wavefront (i.e., beam 26) that emerges fromcollimation optics 156 and direct beam 26 toward objective lens 114. Ifbeam 26 emerges from collimation optics 156 as a diverging wavefront,and the diverging wavefront enters objective lens 114, beam 26 will cometo a focus further from objective lens 114 than the focal point of acollimated beam 26. On the other hand, if beam 26 emerges fromcollimation optics 156 as a converging wavefront, beam 26 will come to afocus closer to objective lens 114 than the focal point of a collimatedbeam 26. In this way, positioning of beam 26 along the optical axis 27may be achieved by moving focusing lens assembly 152 of seconddivergence modulator 48. In some embodiments, focusing lens assembly 152has a lower mass than objective lens 114 and chuck 18, thereby enablingfocusing lens assembly 152 to be moved with a higher speed than movingobjective lens 114 and/or chuck 18 with a comparable amount of power.The faster movement of focusing lens assembly 152 enables a higher speedpositioning of focal point 28 within resin 22.

In embodiments using second divergence modulator 48 to control aposition of beam 26 along the optical axis 27, objective lens 114 ispreferably designed to handle a range of entering wave fronts, which canimprove the quality of the voxels formed within resin 22.

In some embodiments, second divergence modulator 48 may introduceaberrations into beam 26. The aberrations may also be utilized tocompensate for aberrations introduced near image plane 14. In someembodiments, an immersion objective may be used to compensate foraberrations introduced near image plane 14. However, in embodiments thatsimply use a dray air objective, spherical aberrations may exist when avoxel is formed at certain depths (measured along the z-axis direction)within resin 22. In such embodiments, the spherical aberrations may beactively compensated for with proper design of second divergencemodulator 48, such as by introducing opposite amounts of sphericalaberration in collimation optics 156. Compensating for aberrations mayhelp form substantially high quality voxel at a wide range of depthswithin resin 22.

In some embodiments, it may be preferred to use two or more of theabove-described methods to scan the focal point 28 of beam 26substantially along the optical axis 27. For example, mechanicalscanning on the objective lens 114 may be utilized along with the seconddivergence modulator 48 to provide enhanced positioning control of focalpoint 28 substantially along the optical axis 27, such as, for example,an extended range of optical axis 27 control.

Optical system 11 may also include other, optional modules. Each of theoptional modules will be described in further detail below, and FIG. 12illustrates an optical system 161 including all of the optional modules.

Optical system 161 may include an optional power dump module 163following the light source 32. The power dump module 163, as the nameimplies, is a sub-system capable of reducing the power of the beam 26output from light source 32 to a desired level, such as, for example, alevel that will not damage the subsequent optical components in theoptical system 11, or approximately a level desired to initiate cure ofresin 22. The power dump module 163 may not be necessary in allembodiments, such as those utilizing a light source 32 that emits a beam26 of desired power for the intended application.

In one embodiment, illustrated in FIG. 13, the power dump module 163includes a polarizing beam splitter (PBS) 171, an optional second PBS175, and a half waveplate 173. A linearly polarized light beam 26 exitsfrom the light source 32 and passes through the first PBS 171. The beam26 then passes through a half waveplate 173 before encountering a secondPBS 175. By controlling the rotation of the waveplate 173 with respectto the second PBS 175, the amount of beam 26 that is directed by thesecond PBS 175 to the subsequent components of the optical system 11 maybe varied.

Optical system 161 may further include another monitor system, referredto herein as beam quality camera and power monitor 165. The beam qualitycamera and power monitor 165 is used to monitor at least one of thepower, shape or position of beam 26 at the location within opticalsystem 11 from which beam 26 is sampled. The beam quality camera andpower monitor 165, as shown in FIG. 14, includes a beam sampling mirror181 that reflects a small fraction 26 a of beam 26 and transmits theremainder of beam 26. The fraction 26 a reflected by the beam samplingmirror 181 is routed through a beam splitter 183 that sends a firstportion 26 b of the small fraction 26 a to a power detector 185 and asecond portion 26 c of the fraction 26 a to a shape and position sensor187 capable of detecting a shape and position of beam 26, such as, forexample, a charge-coupled device (CCD), a CMOS-based camera, or anotherphotodiode-based sensor. The power detector monitors the power of thefirst portion 26 b of the beam 26 at this point in the optical system161, and the shape and position sensor 187 monitors the shape andposition of the second portion 26 c of beam 26. Even though the power ofonly the first portion of beam 26 is monitored, the beam quality cameraand power monitor module 165 may use algorithms to estimate the totalpower of beam 26 at this point in the optical system 161. In onepreferred embodiment, the power detector is available from NewportCorp., Irvine, Calif., under the trade designation Newport 818 SL.

The power detector 185 and shape and position sensor 187 output signalsbased on the monitored power, shape and position of beam 26 which may beused by control module 12 to determine whether the power, shape, andposition of beam 26 is within an acceptable range of the desiredcharacteristics at this point in the optical system 161. The controlmodule 12 may then control components of optical system 161 (e.g., firstdivergence modulator 38, power control 40, or the like) to produce adesired adjustment to one or more of the power, shape, and position ofbeam 26 in response to the signal output by the beam quality camera andpower monitor module 165.

The optical system 161 may further include a dispersion module 167 formonitoring and correcting any unwanted dispersion (i.e., widening of thepulse width) in beam 26. Dispersion module 167 may include a monitorsystem, group velocity dispersion (GVD) monitor 191, and a sub-systemcapable of modifying the dispersion of beam 26, which may include acontrol module 195 and dispersion compensated optics 193, as shown inFIG. 15.

The temporal characteristics of beam 26 generally affect the intensityof beam 26. For example, if light source 32 provides a femtosecond beam26, group velocity dispersion (GVD) may result as beam 26 propagatestoward image plane 14, which may decrease the peak intensity of beam 26,such that when beam 26 reaches resin 22, beam 26 no longer exhibits thesufficient threshold intensity to initiate cure of resin 22. Afemtosecond pulse is typically composed of various frequencies that maycover a large bandwidth depending on the temporal pulse width. As thesefrequencies propagate through optical system 11, the longer wavelength(or “red”) light travels faster than the shorter wavelength (or “blue”)light. This may be referred to as GVD.

GVD has the effect of lengthening the pulse width in time, which may bean undesirable effect. GVD may be measured by dispersion module 167using a GVD monitor 191. One common GVD monitor includes anautocorrelator. An autocorrelator takes an incoming pulse, splits itwith an interferometer, and sends one portion along a variable delaypath and the second portion along a set path length. The two portionsare then sent through a crystal to create a nonlinear process known assecond harmonic generation (SGH). The SGH light energy versus thevariable time delay results in the measurement of the pulse width.However, autocorrelators possess disadvantages which limit theirapplicability in optical systems. Disadvantages include high sensitivityto alignment, assumptions made about the shape of the pulse that maylimit details about the original pulse, and a lack of intensity or phasemeasurement. Because of these disadvantages, another type of GVD monitor191, such as a Frequency-Resolved Optical Gating (FROG) or aGrating-eliminated no-nonsense observation of ultrafast incident laserlight e-fields (GRENOUILLE) may monitor the dispersion of beam 26. FROGmeasures signal spectrum versus time delay rather than energy versustime delay. This allows the measurement to determine the pulse width,intensity, and relative phase of the pulse. However, FROG is morecomplex, and thus typically more expensive that a conventionalautocorrelator. GRENOUILLE is a less complex FROG device that has nomoving parts and is insensitive to alignment, and still measures fullphase and intensity data of a pulse.

To correct for GVD, dispersion module 167 may precompensate or correctbeam 26 using dispersion compensated optics 193, such as prisms,gratings (standard diffractive or fiber based), chirped coatings onmirrors or optical filters that modify the spectral phase of the beam,such as a Gires-Tournois interferometer or a specially designed cascadedchain of Mach-Zehnder interferometers, whereby the optics are composedsuch that the red light must take a longer optical path that the bluelight through these dispersion compensated optics. In this manner, theblue light becomes sufficiently far ahead of the red light in time suchthat as all the colors pass through the remaining optical system 11,substantially all colors arrive at image plane 84 at the same time tomaintain the ultrafast pulse width out of the femtosecond beam 90. Theamount of pre-compensation or correction may be based on signals outputby the GVD monitor 191 and may be controlled by control module 12 oranother appropriate control module, such as a control module 195dedicated to the dispersion module 167.

Some light sources 32 include controllable dispersion compensationfeatures built into the light source 32 itself. In embodiments usingthese light sources 32, additional dispersion compensation optics may ormay not be desired or necessary depending on the design and constructionof optical system 11.

Control of the dispersion characteristics of beam 26 may also be used tocontrol the power of beam 26. For example, by increasing the amount ofdispersion of beam 26, the power of focal point 28 of beam 26 may bedecreased. Conversely, by decreasing the amount of dispersion of beam26, the power of focal point 28 of beam 26 may be increased. However,this method may not be preferred in some embodiments, because preciselycontrolling the dispersion of beam 26 may be difficult.

Optical system 161 may also include an optional focal plane viewingmodule 169 to monitor the pulsewidth and location of beam 26 after beam26 leaves objective lens 114. The monitoring and control of thepulsewidth of the beam 26 is difficult to accomplish because there arefew available devices that can detect a pulsewidth after the beam 26passes through the final objective 114. The focal plane viewing module169 allows for relative measurement of the pulsewidth of beam 26 bymonitoring a material that fluoresces when exposed to beam 26. Forexample, assuming all other variables are constant, when a higherfluorescence is detected, it may be inferred that the pulsewidth isrelatively shorter than when a lower fluorescence is detected, because ahigher fluorescence implies a higher intensity of beam 26, which impliesa shorter pulsewidth.

The focal plane viewing module 169 may also enable the tracking of thefocal point 28 in the x-y plane (see FIG. 1). The fluorescence isconfined substantially to the volume of resin 22 located at focal point28 of beam 26, so any movement of focal point 28 produces acorresponding movement of the source of fluorescence within resin 22.Thus, by using a detector that has spatial resolution in the x-y axes,the position of the fluorescing portion of resin 22, and thus the focalpoint 28, may be tracked in the x-y axes.

One such suitable detector includes a quadrant detector, which in someembodiments includes four silicon chips that indicate the position ofbeam 26 in the x-y plane (the plane normal to the optical axis 27) basedon the voltage outputted by the silicon chips in each quadrant. Anothersuitable detector may include an array of photodiodes.

The focal plane viewing module 169 may be inserted at many locationswithin the optical system 161, and may receive light fluorescing fromresin 22 via, for example, a beam splitter, a beam sampling mirror orthe like.

It may also be necessary to calibrate both the beam 26 power and focalpoint 28 location within optical system 11, 161 (hereinafter “opticalsystem 11”). Thus, exposure system 10 (FIG. 1) may include a calibrationmodule 210, which is illustrated in FIG. 16. Calibration module 210 mayinclude a number of sub-modules, including, for example, a slow shutter211, a power meter 212, a chuck mounted power meter 213, a chuck mountedposition sensing device (PSD) 214, and a control module 215. Controlmodule 215 generally controls calibration module 210. In one embodiment,control module 215 includes a processor, such as a microprocessor, acontroller, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA),discrete logic circuitry, or the like. In some embodiments, theprocessor may implement software, hardware, firmware or a combinationthereof to control slow shutter 211, power meter 212, chuck mountedpower meter 213 and chuck mounted PSD 214. In other embodiments,calibration module 210 may not include a control module 215 and insteadmay be controlled by control module 12 of exposure system 10, or controlmodules 12, 215 may be used in combination to control calibration module210.

One optical component that allows for calibration of both power of beam26 and location of focal point 28 without exposing resin 22 to beam 26includes a slow shutter 211. The slow shutter 211 may include amotor-driven mirror that may be moved from an open position to a closedposition. In some embodiments, slow shutter 211 is slower thanhigh-speed shutter 44, that is, slow shutter 211 may respond to an inputmore slowly than high-speed shutter 44. Slow shutter 211 may bepositioned at any point within optical system 11, and in someembodiments, it may be preferred that slow shutter 211 is located at apoint near the end of optical system 11 (e.g., as near to the finaloptical element of optical system 11 as possible). Positioning slowshutter 211 near the end of optical system 11 may allow measurement of apower of beam 26 that is more representative of the power of beam 26 atthe image plane 14 than if slow shutter 211 is positioned near thebeginning of optical system 11. This is because many optical elementsmay be expected to affect the power of beam 26, and thus, fewer opticalelements between slow shutter 211 and the end of optical system 11 willresult in less potential change in the power of beam 26 between slowshutter 211 and focal plane 14.

When the slow shutter 211 is in an open position, beam 26 is allowed topass through the optical system 11 and expose resin 22 under control ofthe other optical components of optical system 11 (e.g., exposurecontrol module 82 and the like). When the slow shutter 211 is in aclosed position, slow shutter 211 redirects beam 26 to a power meter212, which measures the power of beam 26. The power meter 212 may be anysuitable power meter including, for example, a multimeter, whichincludes a silicon chip that outputs a voltage indicative of power. Insome embodiments, the power meter 212 is a National Institute ofStandards and Technology-traceable power meter.

The power meter 212 may send its output to control module 215. Controlmodule 215 may use the output of the power meter 212 to calibrate thepower of beam 26. For example, control module 215, or control module 12of exposure system 10, may compare the outputs of power meter 212 anddigital camera 64 or the power meter of power control 40. Control module215 may perform the comparison at a single point and adjust the outputof digital camera 64 or the power meter of power control 40 to match theoutput of power meter 212, or may perform the comparison at a pluralityof output settings of light source 32 and generate a calibration curvethat correlates the power indicated by digital camera 64 or the powermeter of power control 40 to the power measured by power meter 215. Thismay allow more accurate measurement of the power of beam 26 at thevarious points in optical system 11 where digital camera 64 and/or thepower meter of power control 40 are located and a more accuratecomparison of the measure power values. Calibration of actual deliveredpower may improve the fidelity of articles formed in resin 22 usingoptical system 11 and may also help ensure repeatability and processconsistency over time.

The slow shutter may also allow for the use of the position detector 46to locate focal point 28 with respect to interface 24 without initiatingcure of resin 22. For example, the slow shutter may be located in aposition within optical system 11 such that beam 26 is prevented fromimpinging on resin 22 when the slow shutter is closed, while aninterrogator beam is allowed to interrogate and locate the interface 24of substrate 20 and resin 22.

The system calibration module 210 may also include modules mounted onchuck 18 to calibrate the position and power of focal point 28 and beam26 after beam 26 exits objective lens 114. Specifically, in theillustrated embodiment, chuck mounted power meter 213 and chuck mountedPSD 214 are mounted on chuck 18 to provide information regarding beam 26at the focal plane 14. Power meter 213 and PSD 214 may be mounted at anyuseful location of chuck 18 within the field of view of objective lens114. That is, power meter 213 and PSD 214 may be mounted at any locationof chuck 18 onto which objective lens 114 may focus beam 26.

Calibrating the power and position of beam 26 and focal point 28 at theimage plane 14 allows the effects of the entire optical system 11 to betaken into account. Thus, calibrating the power and position of beam 26and focal point 28 at the focal plane 14 may provide more accuratecalibration than calibration using slow shutter 211 and power meter 212.

Similar to power meter 212, power meter 213 may include a NIST-traceablepower meter such as, for example, a multimeter. The multimeter may bemounted directly on chuck 18, or a collecting lens, which directs beam26 to the multimeter, may be mounted on chuck 18. The multimeter mayoutput a voltage or other signal indicative of the power of beam 26 tocontrol module 215 or another suitable control module, such as controlmodule 12 of exposure system 10. Control module 215 may then use signaloutput by power meter 213 to calibrate digital camera 64, the powermeter of power control 40, or power meter 212 in a similar calibrationroutine to the routine described above with reference to power meter212.

Chuck mounted PSD 214 may calibrate the modules responsible for thepositioning of beam 26, including PSD 62 of each of the first and secondbeam monitors 34, 42, and first and second galvanometers 50, 52. Asdescribed above, the position of beam 26 in the x-y axes of image plane14 may be correlated to positions of first and second galvanometers 50,52. Additionally, the galvanometers 50, 52 may be controlled based on alocation signal output by PSD 62 in each of the first and second beammonitors 34, 42. Thus, it is important to have an accurate calibrationbetween the position sensed by PSD 62 in each of the first and secondbeam monitors 34, 42, the position of the first and second galvanometers50, 52, and the actual location of beam 26 at the image plane 14, asmeasured by chuck mounted PSD 214. As such, control module 215, oranother suitable control module, such as control module 12 of exposuresystem 10, may utilize the location signal output by chuck mounted PSD213 to calibrate the PSD 62 of each of the first and second beammonitors 34, 42 and first and second galvanometers 50, 52. For example,PSD 213 may detect the position of beam 26 and output a location signalincluding two coordinate values (e.g., an x-axis coordinate value and ay-axis coordinate value, or a radial coordinate value and an angularcoordinate value (in a polar coordinate system)). Control module 215 maycompare these coordinate values to the coordinate values indicated byPSD 62 of each of the first and second beam monitors 34, 42, and thecoordinate values input to first and second galvanometers 50, 52, whichmay or may not be the same. The difference between these coordinatevalues, if any, may indicate a calibration error, which the controlmodule 215 may correct by updating the coordinate values of PSD 62and/or galvanometers 50, 52 to match those of PSD 213. This process maybe repeated for a plurality of coordinate values measured by PSD 213 toproduce a more accurate calibration of PSD 62 of each of the first andsecond beam monitors 34, 42, first and second galvanometers 50, 52, andthe actual position of beam 26 in the x-y plane of the image plane 14 asmeasured by the chuck mounted PSD 213.

Each of the power and position calibration routines may be repeatedperiodically throughout the manufacture of an article, or at timesbetween manufacture of articles, to help ensure the stability ofexposure system 10 and fidelity of the manufactured articles to thedesired articles.

Control module 12, or any other suitable control module, may includesoftware and/or hardware that enable control of exposure system 10 andthe various optical modules to accurately generate the desired featuresfor the finished article. The software and/or hardware may include anumber of control system levels to manage various levels of exposuresystem 10. For example, the software and/or hardware may include afeature control system, a supervisory control system, and a high speedhigher level control system.

The feature control system includes a high speed integrated controlsystem to control the exposure of resin 22 to beam 26. The featurecontrol system may control exposure control module 82, optical scanningmodule 110 and interface with the first and second beam monitors 34, 42,position detector 46, and system calibration module 210 to providecoordinated position and exposure control in the x-, y-, and z-axes. Thefeature control system may collect actual beam 26 position and desiredbeam 26 position data for all three axes, and may control theresponsible optical modules to move beam 26 into the desired position.

The high speed higher level control system interfaces with all modulesof exposure system 10 and provide overall supervision of articlegeneration, optical diagnostics, and system sequencing.

The environment within which the system is operated may limit theperformance of exposure system 10. For example, variations intemperature, humidity and electrical power, along with vibration andparticulate contamination, may be detrimental to the process ofmanufacturing articles using exposure system 10. Thus, it may bedesirable to control the environment in and around exposure system 10.One or more of temperature, humidity, and particulate content may becontrolled in and around the exposure system 10. For example, the system10 may be housed in a clean room that provides a Class 1000 or betterclean environment. The surrounding environment may also includetemperature control to limit the range of temperatures system 10experiences. For example, in some preferred embodiments, temperaturecontrol of better that +/−0.1° C. may be provided. Humidity may alsoaffect the ability of exposure system 10 to create articles with highfidelity to the desired article. In some embodiments, control of betterthan +/−10% relative humidity may be provided to reduce or substantiallyeliminate the influence of humidity fluctuations on system 10 andarticle produced thereby.

Unexpected or undesired interruptions in the supply of power to exposuresystem may result in wasted articles due to imperfections caused by theabrupt and uncontrolled shutdown of exposure system 10. For example, ifthe galvanometers 50, 52 or high speed shutter 44 are shut down beforelight source 32, a volume of resin 22 may be cured that is not desiredto be cured. Thus, in some embodiments, the system 10 may be connectedto an Uninterruptible Power Supply (UPS) such that in the event of abuilding power failure, the system 10 will transfer to battery powerlong enough to finish at least the current feature being written (butpossibly not the whole article) and go into a soft shutdown thatprevents the exposure of undesired volumes of resin 22. In somepreferred embodiments, the soft shutdown can be restarted after power isrestored without detrimental effects to the part being fabricated.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. An exposure system comprising: a light sourceemitting a beam along an optical axis, wherein the beam is capable ofinducing a multi-photon reaction in a resin; a resin undergoingmultiphoton reaction; and an automated system comprising: a monitor thatmeasures at least one property of the beam selected from power, pulselength, shape, divergence, or position in a plane normal to the opticalaxis, wherein the monitor generates at least one signal indicative ofthe property of the beam; and a sub-system that adjusts the beam inresponse to the signal from the monitor; wherein the beam inducespolymerization in the resin by a multi-photon absorption process.
 2. Theexposure system of claim 1, wherein the resin is substantiallytransparent to a wavelength of the beam.
 3. The exposure system of claim1, wherein the monitor comprises a first monitor and a second monitor.4. The exposure system of claim 1, wherein the monitor comprises adivergence monitor that monitors at least one of a shape and adivergence of the beam.
 5. The exposure system of claim 1, wherein themonitor comprises a monitor system that detects the position of the beamin a plane normal to the optical axis and also detects a position of afocal point of the beam along the optical axis.
 6. The exposure systemof claim 1, wherein the sub-system comprises a controller.
 7. Theexposure system of claim 1, wherein the sub-system comprises a beamsteering module.
 8. The exposure system of claim 7, wherein the beamsteering module comprises at least one piezoelectric actuated mirror. 9.The exposure system of claim 1, wherein the sub-system comprises adivergence modulation system.
 10. The exposure system of claim 9,wherein the divergence modulation system comprises a piezo-electricdevice.
 11. The exposure system of claim 9, wherein the divergencemodulation system comprises at least two elements each having an opticalpower.
 12. The exposure system of claim 1, wherein the sub-systemcomprises a power control system.
 13. The exposure system of claim 1,wherein the sub-system comprises a high speed shutter.
 14. The exposuresystem of claim 13, wherein the high speed shutter comprises a Pockelscell.
 15. The exposure system of claim 13, further comprising a secondshutter for calibrating a characteristic of the beam, the second shutterbeing slower than the high speed shutter.
 16. The exposure system ofclaim 1, wherein the sub-system comprises a galvanometer systemcomprising at least one galvanometer-mounted mirror.
 17. The exposuresystem of claim 1, further comprising an objective lens for focusing thebeam at a position within the resin.
 18. The exposure system of claim 1,further comprising a sample holding system for holding and positioningthe resin and reducing the effects of at least one of temperature andvibration on the resin.
 19. The exposure system of claim 1, wherein thebeam comprises a wavelength in a range from about 400 to 2000 nm. 20.The exposure system of claim 1, wherein the beam comprises a wavelengthin a range from about 500 to 1000 nm.
 21. The exposure system of claim1, wherein the beam comprises a wavelength in a range from about 750 nmto about 850 nm.
 22. The exposure system of claim 1, wherein the beamcomprises a pulse width less than about 10 ns.
 23. The exposure systemof claim 1, wherein the beam comprises a pulse width less than about 10ps.
 24. The exposure system of claim 1, wherein the beam comprises apulse width less than about 100 fs.
 25. An exposure system comprising: alight source emitting a beam substantially at a first wavelength alongan optical axis, wherein the beam induces polymerization in a resin thatis substantially optically transparent at the first wavelength; a firstbeam monitor system, wherein the first beam monitor systems monitors afirst characteristic of the beam and generates a first signal, whereinthe first characteristic comprises at least one of a power, a shape, anda position of the beam in a plane normal to the optical axis of thebeam; a first divergence monitor system monitoring a divergence of thebeam; a first divergence modulation system adjusting at least one of adivergence and a shape of the beam; a first power control systemadjusting a power of the beam at a first speed; a second monitor system,wherein the second monitor system monitors the first characteristic ofthe beam and generates a second signal, wherein the first and secondsignals are used to adjust the first characteristic; a first shuttertransmitting or blocking the beam for controlling exposure of the resin;a third monitor system monitoring a position of a focal point of thebeam along the optical axis; a second divergence modulation systemadjusting at least one of a divergence and a shape of the beam; a firstgalvanometer system scanning the beam at a second speed not greater thanthe first speed, the scanning being along a first directionsubstantially normal to the optical axis; a second galvanometer systemscanning the beam at a third speed not greater than the first speed, thescanning being along a second direction substantially normal to theoptical axis and different from the first direction; an objective lenssystem for focusing the beam at a position within the resin; and asample holding system for holding and positioning the resin and reducingthe effects of at least one of temperature and vibration on the resin.26. The exposure system of claim 25, wherein the first wavelength is ina range from about 750 nm to about 850 nm and a pulse width of the beamis less than about 100 femtoseconds.
 27. The exposure system of claim25, wherein the first divergence modulation system comprises at leasttwo elements each having an optical power.
 28. The exposure system ofclaim 25, further comprising a second shutter for calibrating the firstcharacteristic of the beam, the second shutter being slower than thefirst shutter.
 29. The exposure system of claim 25, wherein the seconddivergence modulation system comprises a piezo-electric device.
 30. Theexposure system of claim 25, further comprising a first dispersionsystem at least partially compensating for a dispersion of the beam. 31.The exposure system of claim 25, wherein the first shutter comprises aPockels cell.